One type of a hall-point pen uses a decolorable ink. In addition, one type of a printer forms an image with a decolorable toner. The images written with the pen or formed with the printer can be erased by heating a sheet having the images. The image written with the ball-point pen can be erased, for example, with frictional heat. The image formed with the printer can be erased, for example, by heating the sheet with an erasing apparatus having a heater.
Such an erasing apparatus separates sheets on which images are successfully erased from sheets on which images cannot be erased, so that the sheets from which the images have been erased can be reused.